Molten



April 3o, 1957 F. B. SELLERS ET AL REDUCTION OF METAL. OXIDES FiledMarch 17, 1954 TOR N E' V15 2,790,71 l Ice -vP-atented Apr. 30, 1957REDUCTION OF METAL OXIDES Frederick Burton Sellers, Tarrytown, N. Y.,and Peter L.

Pauli, Norwalk, Conn., assignors to Texaco Development Corporation, NewYork, N. Y., a corporation of Delaware Application March 17, 1954,Serial No. 416,815

4 Claims. '(Cl. 'l5-41) This invention relates to a process of reductionof a metal oxide with carbon monoxide and hydrogen. In one of its morespecific aspects, this invention relates to a process for the productionof metallic iron or pig iron by the reduction of an iron oxide,particularly iron ore, with carbon monoxide and hydrogen.

In the process of the present invention a reducible metal oxide in lumpform is contacted with a mixture of carbon monoxide and hydrogen at atemperature sufcient to cause reduction of the metal oxide to metal andfusion of the resulting metal. The reduction of the solid metal oxide tomolten metal takes place in a reduction furnace in which a downwardlymoving bed of the metal oxide is maintained. The metal oxide is chargedto the top of the bed and the molten metal drawn from the bottom. Areducing gas is introduced near the bottom of the bed and passed upwardcountercurrent to the ilow of the metal oxide. The reducing gas isgenerated from any suitable fuel by reaction with oxygen. Among thesuitable fuels are included hydrocarbon gases, oil, oil shale, coke andany of the various grades of coal, including lignite, anthracite andbituminous coal.

The present invention is particularly'suited to the production of pigiron from iron ore. In the production of pig iron in a conventionalblast furnace, coke and iluxing agents, generally limestone, are addedto the furnace with the ore. Air is introduced at the base of the blastfurnace, to consume the coke and generate carbon monoxide which, inturn, reduces the ore. The process of the present invention differs fromconventional blast furnace operations in that at least a portion of thereducing gas required in the furnace is generated in a separate gasgenerator; in many cases it is desirable to generate all of the reducinggases in the gas generator.

By the process of this invention, part or all of the coke required forconventional blast furnace operations may be eliminated. This representsa tremendous practical advantage, as a number of sources of high gradeiron ore are situated at a great distance from a source of coking coal.The production of pig iron may now be made independent of coking coals.

A number of processes for the generation of carbon monoxide and hydrogenfrom various fuels are known. In the process of this invention thecarbon monoxide and hydrogen are generated by partial combustion of thefuel with an oxygen-containing gas. While air may be used as theoxygen-containing gas, relatively pure oxygen is preferred. Steam ispreferably used in combination with the oxygen for all of the fuelsexcept gaseous hydrocarbons. The reducing gas generator Vis operated ata temperature within the range of from about 2,000 F. to about 3,000 F.,preferably at a temperature above about 2,200 F. and suilcient to insurethat the metal and slag are in molten` form. In the production of pigiron, a reducing gas temperature ofabout 2,400 F. is about the minimumtemperature required when all of the reducing gas is generated outsidethe ore reduction furnace.

A flow-type gas generator is preferably used for the generation ofreducing gas for the process of this invention. The ow-type generator ischaracterized by the reaction of the fuel in an unpacked reactor in theabsence of catalyst. When solid fuel is used, the fuel particles aresuspended in the gaseous reactants and the gasification reaction takesplace with the solid particles suspended in reactants and gaseousreaction products. For most successful operation of a generator of thistype for the production of carbon monoxide and hydrogen, the temperaturethroughout the generator must be maintained at a temperature above about2,000 F. The temperature may be as high as 3,000 F., although generallyit is undesirable to maintain the temperature at this level because mostrefractory lining materials rapidly deteriorate at temperatures of 3,000F. and above. Practical considerations, particularly apparatuslimitations, usually limit the operating temperature to 2,600 F. to2,800" F.

Suitable metal oxides which may be treated in this process include theoxides of iron, copper, vanadium, nickel, chromium, manganese andtitanium.

In accordance with a specic embodiment of the present invention, ironoxide is reduced to metallic iron in a cylindrical shaft similar to aconventional blast furnace. Carbon monoxide and hydrogen generated in aseparate reducing gas generator by partial combustion of fuel withoxygen is introduced at a temperature above about 2,400" F., into thelower part of the shaft. These gases ascend countercurrent to thedescending bed of iron oxide, reducing the iron oxide to molten metalliciron.

Unless pure ironoxide is used, it is generally desirable to add afluxing agent mixed with the iron oxide to produce a lluid slag at thebase of the shaft. A ilux is useful to reduce the fusion temperature ofthe slag and to render it more uid. Fluxing agents are known in theblast furnace art. Limestone is generally suitable as llux for ironores, although it may be desirable in some instances, to add iluorspar,silica, alumina, or magnesia to increase the quantity or fluidity of theslag. The kind and amount of flux required may be determined from thecomposition of iron ore as is known in the blast furnace art. Ingeneral, the most satisfactory fusion is obtained when the sum of thelime and magnesia in the feed material is approximately equal in weightto the sum of the alumina and silica. The lime or magnesia may be addedin the form of the carbonates, but should be converted to equivalentquantities of the oxide in determining the quantity of flux required.

When a solid fuel is used in the gas generator, a fluxing material maybe added to the gas generator to lower the fusion temperature and insurea molten fluid ash. The requirements for a satisfactory ux may bedetermined from the composition of the ash, following the foregoing rulefor lluxing ore. With most coals, limestone is a satisfactory fluxingmaterial. Generally, it is desirable to discard the slag from thegenerator; if desired, however, the molten fluid ash from the generatormay be discharged directly into the ore reduction shaft together withthe hot gases.

The reducing shaft may be operated at atmospheric pressure or at anelevated pressure. An elevated pressure is desirable in that itincreases the capacity of the apparatus by speeding up the reactionsinvolved in the reduction of the metal oxide. The gas generatorpreferably is operated at an elevated pressure above about p. s. i. g.and preferably at a pressure of at least 100 p. s. i. higher than thepressure in the reducing shaft.

The reduction of the metal oxide may be carried out lwith carbonmonoxide or hydrogen or mixtures of car bon monoxide and hydrogen inalmost any desired portion.

It has previously been mentioned that when the metal oxide is an ironoxide or iron ore, it is preferable to operate the furnace at atemperature on theorder of 2,500J F. or higher in order that both theiron and slag may be withdrawn in molten form as in conventional blastfurnace operations. The temperature atthe base of the shaft maysometimes exceed the temperature in the. generator. This highertemperature in the shaft may result due to the reaction between the gasand the iron oxide.

In another embodiment of the invention, reducing gas is supplied to aconventional type blast furnace. The blast furnace is charged in theusual manner with iron ore, coke and limestone, but with less than theusual amount of coke. Air, or preferably oxygen, is supplied to theblast furnace in the usual manner, but in less than the usual amount.Since the amount of coke fed to thc blast furnace is less than the usualamount, less oxygen is required for reaction with the coke.y Thedeficiency in the quantity of reducing gas resulting from reduction ofquantity of coke charged to the furnace is made up by supplying hydrogenand carbon monoxide from a separate gas generator'. This operationpermits a reduction in the coke requirements for blast furnaceoperations and permits application of the present invention to existinginstallations of blast furnaces.

ln some instances it may be desirable to charge cera-mic pieces, forexample, pieces of refractory brick, to the furnace to make up for theomission of coke, to provide support for the charge in the reactor andpermit free flow of the gas upwardly through the charge. This has thedisadvantage of requiring fusion of the brick or, alternatively,batchwise operation of the furnace.

An object of this invention is to provide an improved process for thereduction of a metal oxide with carbon monoxide and hydrogen. A furtherobject is to provide a process for the production of pig iron from ironoxide wherein the iron oxide is reduced with gas from an externalsource. A still `further object is to provide an improved process forthe operation of blast furnaces to reduce the requirements 4for highgrade metallurgical coke. Other objects and advantages of the inventionwill be apparent from the following detailed description of theinvention and the accompanying drawings.

Figure l of the drawings illustrates diagrammatically one embodiment ofthe invention as applied to the production of pig iron from ironore.Figure 2 illustrates diagrammatically the application of the process ofthis invention to blast furnace operation.

With reference'to the drawing, thenumeral 5 desigf nates a shaft filledwith iron ore in which the ore is reduced to the molten metal. The oreis preferably reduced in apparatus in the form of a tall vertical columnor shaft slightly larger in diameter at the bottom than at the top.charge to the upper end of the shaft as indicated in the drawing bylines 6 and 7, respectively. Molten iron and slag are tapped off thebottom of the shaft as indicated by line 8.

Reducing gas is generated in a gas generator 11, in which fuel andoxygen are combined to produce a mixture lof carbon monoxide andhydrogen. In this example, the generator is operated at a temperature ofabout 2,6007 F. The resulting stream of hydrogen and carbon monoxide ispassed without cooling through line 12, directly into the lower portionof the shaft. The temperature at which the gas generator is operated ispreferably the maximum temperature which-may be tolerated in thegenerator wtihout unnecessarily shortening the life of its refractorylining.

As the reducing gas from line 12 passes up through the shaft it iscontacted-by the iron oxide and limestone slowlyr descending through theshaft. In the lower portion of the furnace, the ironoxideissubstantially completely reduced to metallic iron. Oxygen givenup 4by Iron ore and limestone are introduced as the iron oxide duringits reduction converts the carbon monoxide and hydrogen ascendingthrough the shaft to carbon dioxide and steam. Only a part of theascending gas stream is oxidized, so that `some carbon monoxide andhydrogen is -still present in the upper portion of the shaft. Gases arevented from the upper part of the shaft through line 13. These gasescontain considerable quantities of heat which maybe used for thegeneration of steam.

Air or oxygen may be introduced into the upper portieri of the furnacethrough line 14, for combustion of the unreacted carbon monoxide andhydrogen. Burning these gases in the upper part of the furnace preheatsthe incoming charge of iron ore and limestone. It is generally desirableto recirculate gas from an intermediate point in the shaft to the gasgenerator. This is indicated in the drawings by line 15. The recyclestream may range as high as about 7() percentof the gases .ascendingthrough the shaft.

Sulphur may be removed from the reducing gas before it is introduced tothe shaft. Sulphur removal may be effected by passing the hot reducinggas stream over iron or limestone. VIn the process of the invention itis preferable to pass the gas through a bed of limestone, or calciumoxide, for sulphur removal. The calcium oxide may be subsequently`charged to the shaft with the ore and the sulphur removed therefrom byvburning with the air or oxygen introduced through line 14. Removal ofsulphur from the reducing gas is desirable when the fuel supplied to thesynthesis gas generator contains an appreciable amount of sulphur, suchas, for example, coal, oil shale, sour natural gas, or a sourhydrocarbon oil.

Figure 2 of the drawings illustrates the application of the principlesof my invention to the production of pig iron in a conventional blastfurnace. A blast furnace 16 is charged with a mixture of iron ore, coke,and a iluxing material, for example, limestone. In accordance with thisinvention, less than the usual amount of coke is used which, in turn,reduces the limestone requirements. Thus the charge to the furnace isricher in iron ore than is the charge to the conventional blast furnace.Molten iron and slag are tapped from the lower portion of the blastfurnace in the usual manner. Air or other oxygen-containing gas,preferably relatively pure oxygen, is introduced to the blast furnacethrough the usual tuyeres 17. Gases are vented lfrom the upper end ofthe furnace through line 18.

A stream of reducing gas, comprising carbon monoxide, is generated in areducing gas generator 19 by partial combustion of a carbon-containingfuel with an oxygencontaining gas, preferably relatively pure oxygen.These gases are introduced through line 20 into the blast furnace at anintermediate point, above the point of introduction of air. A part ofthe gases may be recycled from the upper portion of the blast furnacethrough line 21 to the reducing gas generator. These gases containcarbon dioxide and water vapor resulting from oxidation of hydrogen andcarbon monoxide with oxygen given up by the ore. In the reducing gasgenerator, the carbon dioxide and water vapor are again converted tocarbon monoxide and hydrogen.

It will be evident that, by supplying an auxiliary stream of reducinggas from an external generator to the blast furnace, economies :arerealized due to the savings of high grade coke. When the limestonecharged to the shaft has been previously used for removing sulphur fromthe gases from the reducing gas generator, the sulphur may be eliminatedfrom the limestone by introducing air or oxygen to the furnace aspreviously described. This converts the sulphur associated with thelimestone or iron ore to sulphur dioxide which is discharged from theshaft with the vent gases.

Example 1 Iron ore `containing 63 weightpercent iron is reduced in ashaft using a limestone containing about 95 percent calcium carbonate asa ux. Ore is charged at the rate of 4.25 tons per hour, mixed with about1,200 pounds of limestone. The ore is reduced with a stream of carbonmonoxide and hydrogen from a separate gas generator, the operation ofwhich is described more fully hereinafter.

The furnace is operated at a pressure of about 200 pounds per squareinch gauge and with a hearth ternperature (botton of shaft) of 2,700 F.The furnace produces about 2.7 tons of pig iron per hour containingabout 99 weight percent metallic iron and only about 0.01 weight percentsulphur. Molten iron and slag are tapped from the base of the furnace asin conventional blast furnace operations.

Hot reducing gas is produced in a flow-type coal-fired gas generator. Adispersion of powdered coal in steam is reacted with commercially pureoxygen in an unpacked reaction zone containing no catalyst or packing.Bituminous coal having the following proximate analysis is used.

Weight percent The coal contains about 0.4 weight percent sulphur.

Commercial oxygen obtained by air rectification and analyzing about 95.3volume percent oxygen is supplied to the generator. Approximately oneton of coal per fhour is fed to the generator, together with about 110pounds of steam and 20,000 standard cubic feet of oxygen. The oxygen,steam and coal are preheated to a temperature of about 1,000 F. Theresulting generator temperature is about 2,700 F. The hot gas from thegenerator is passed without preliminary treatment directly to the orereduction furnace.

A stream of gas is withdrawn from an intermediate point in the orereduction shaft and recycled to the generator. This gas contains about24 volume percent water vapor and has the following approximate analysison a dry basis.

Volume percent Hydrogen 10.5 Carbon monoxide 40.8 Carbon dioxide 45.8Nitrogen 2.9

The recycle gas stream amounts to about 138,000 cubic feet per hour.

The gas from the generator has the following approximate analysis on adry basis.

Volume percent Hydrogen 14.8 Carbon monoxide 56.9 Carbon dioxide 25.5Nitrogen 2.8

Example 2 Iron ore containing 63 weight percent iron is mixed with cokeand with limestone containing 97 weight percent calcium carbonate. Themixture is charged into a conventional type blast furnace in thevfollowingproportions:

Lbs/hr.

Iron ore 6000 Limestone 965 Coke 1950 Oil lbs./hr 747 Steam lbs./hr 211Oxygen S. C. F. H..- 8030 The oil and steam are preheated to 730 F.;high purity oxygen is supplied at ambient temperature.

The reducing gas has the following composition:

Volume percent Hydrogen 46.0 Carbon monoxide 44.8 Carbon dioxide 2.7Nitrogen 0.7 Methane 1.2 Hydrogen sulfide 0.5 Water 4.1

The temperature of the gas generator is about 2,600 F. The reducing gasis introduced finto the blast furnace at the rate of 37,950 S. C. F. H.The gases are introduced above the tuyeres and below the point at whichthe temperature of the furnace is below 2,000 F.

A pressure of 350 pounds per square inch gauge is maintained in the gasgenerator. The pressure at the inlet to the blast furnace is in therange of 5 to 40y p. s. i. g. Pressure reduction between the generatorand the blast furnace inlet takes place across an Alundunx sleeve 0.6inch inside diameter.

Iron and slag are tapped from the furnace in conventional manner at therate of 3,785 pounds of iron and 1,310 pounds of slag per hour.

By way of comparison, reduction of the iron ore by conventional blastfurnace operation to produce the same amount of pig iron requires 3,070pounds of coke and a considerable increase in limestone.

Operation of the gas generator at a pressure considerably higher thanthe pressure in the blast furnace, e. g., to 500 p. s. i. higher thanthe blast furnace pressure, is an important feature of our invention.The difference in pressure between the gas generator and the blastfurnace produces a high velocity jet of reducing gas at its point ofintroduction to the blast furnace. This insures deep penetration of theblast of reducing gas into the ore bed. A deLaval type nozzle (aconvergentdivergent nozzle) may be used to impart maximum velocity tothe jet of reducing gas. The velocity of the stream of reducing gas :atthe point of pressure reduction is preferably in excess of about 1,000feetper second.

We have found that an auxiliary reducing gas suitable for use in a blastfurnace may be produced by partial oxidation of a carbonaceous fuel atatemperature of 2,000 to 3,000 F., preferably at a temperature of 2,400to 2,800 F. We have also found that a satisfactory reducing gas streammay be prepared by reacting a hydrocarbon fuel oil with substantiallypure oxygen and with from about 20 to about 40 weight percent steambased on the weight of the oil. The resulting reducing gas contains fromabout 2 to about 8 percent steam and from about l to 4 percent carbondioxide by volume. It is preferable to maintain the water content of thereducing gas stream within the range of 2 to 4 percent by volume.

This, application is acontinuation-,in-partof our application Serial No.264,158, tiled December 29, 19,51, now abandoned.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas'are indicated in the appended claims.

We claim:

1. In a process for the reduction of iron oxide to molten metallic ironwherein iron oxide admixed with coke and a fluxing material is contactedin an elongated vertical reduction zone with an upwardly owing stream ofreducing gas comprising carbon monoxide whereby the iron oxide isreduced to molten iron, and an oxygen-contai ning gas is introduced intothe lower portion of said reduction zone whereby coke-is converted tocarbon monoxide, the improvement which comprises generating an auxiliarystream of reducing gas comprising carbon monoxide and hydrogencontaining not morev than 8 percent steam and not more than 4 percentcarbon dioxide by volume by reaction of a hydrocarbon fuel oil with anoxygen-containing gas and from about 20 to about 40 Weight percent steambased on the weight of said oil at a temperature within the range offrom about 2,000 F. to about 3,000" F. in a separate gas generationzone, and introducing said auxiliaryA stream of reducing gassubstantially at said A8 reaction temperature directly into saidreduction zone at a point above the point of introduction of saidoxygencontaininggasto the reduction zone.

2. A process as defined in claim 1 wherein said auxiliary stream ofreducing gas is generated at a pressure at least p. s. i. higher thanthe pressure in said reduction zone and said stream of gas passedthrough a zone of restricted cross-sectional area imparting a velocity nexcess of 1,000 feet per second to said stream.

3. A process as defined in claim 1 wherein said auxiliary stream ofreducing gas contains not more than 4 percent steam by volume.

4. A process as defined in claim 1 wherein said oxygencontaining gas issubstantially pure oxygen.

References Cited in the file of this patent UNlTED STATES PATENTS1,485,745 Van Nuys Mar. 4, 1924 1,728,784 Christiansen Sept. 17, 19292,420,398 Kinney May 13, 1947 2,577,730 Benedict et al Dec. 1l, 19512,672,488 Jones Mar. 16, 1954 FOREIGN PATENTS 7,556 Australia May 30,1927 8,057 Great Britain of 1893

1. IN A PROCESS FOR THE REDUCTION OF IRON OXIDE TO MOLTEN METALLIC IRONWHEREIN IRON OXIDE ADMIXED WITH COKE AND A FLUXING MATERIAL IS CONTACTEDIN AN ELONGATED VERTICAL REDUCTION ZONE WITH AN UPWARDLY FLOWING STREAMOF REDUCING GAS COMPRISING CARBON MONOXIDE WHEREBY THE IRON OXIDE ISREDUCED TO MOLTEN IRON, AND AN OXYGEN-CONTAINING GAS IS INTRODUCED INTOTHE LOWER PORTION OF SAID REDUCTION ZONE WHEREBY COKE IS CONVERTED TOCARBON MONOXIDE, THE IMPROVEMENT WHICH COMPRISES GENERATING AN AUXILIARYSTREAM OF REDUCING GAS COMPRISING CARBON MONOXIDE AND HYDROGENCONTAINING NOT MORE THAN 8 PERCENT STREAM AND NOT MORE THAN 4 PERCENTCARBON DIOXIDE BY VOLUME BY REACTION OF A HYDROCARBON FUEL OIL WITH ANOXYGEN-CONTAINING GAS AND FROM ABOUT 20 TO ABOUT 40 WEIGHT PERCENT